If you already have a file checked in, and you want to ignore it, Git will not ignore the file if you add a rule later. In those cases, you must untrack the file first, by running the following command in your terminal:

git rm --cached FILENAME

Create a global .gitignore

You can also create a global .gitignore file, which is a list of rules for ignoring files in every Git repository on your computer. For example, you might create the file at ~/.gitignore_global and add some rules to it.

Explicit repository excludes

If you don't want to create a .gitignore file to share with others, you can create rules that are not committed with the repository. You can use this technique for locally-generated files that you don't expect other users to generate, such as files created by your editor.

Use your favorite text editor to open the file called .git/info/exclude within the root of your Git repository. Any rule you add here will not be checked in, and will only ignore files for your local repository.